Synthesis of [1.1.1]Propellanes by Bridging of Bicyclo[1.1.0]butanes

Several [1.1.1]propellanes were synthesized by bridging the 1,3‐positions of the corresponding bicyclo[1.1.0]butane. The synthesis of 1‐bromo‐3‐(chloromethyl)bicyclobutanes and the bridging were carried out in a one‐pot reaction by addition of 2.0 equiv. of MeLi to 1,1‐dibromo‐2,2‐bis(chlormethyl)‐cyclopropanes 10. Three routes to 10 were investigated: Firstly, the Wittig reaction of 1,3‐dichloroacetone leading to (chloromethyl)allyl chlorides 6 was, with the exception of 6m, successful only with Wittig reagents derived from primary alkyl halides, Secondly, reduction of diethyl alkylidenemalonates with LiAlH4 in benzene afforded carbinols 12 which were converted into 6 by reaction with N‐chlorosuccinimide/dimethyl sulfide. The cyclopropanation of 6 to 10 was achieved by reaction with bromoform/NaOH under phase‐transfer catalysis conditions. Finally, starting from diethyl alkylidenemalonates, the sequence of reduction and cyclopropanation could be interchanged, according to the sequence 11 → 13 → 14 → 10. Propellanes 5b and 3 were reduced with LiAlH4 to bicyclo[1.1.1]pentanes 15b and e. 2‐D INADEQUATE NMR spectra of 5d and 5p indicate that the coupling constants J(13C‐13C) between the bridgehead positions are very small, i.e. 0.47 and 0.53 Hz, respectively.